1. Field of the Invention
The present invention relates generally to a contactless data carrier that is attached to various products, is used for a merchandise or process control by storing ID numbers or merchandise characteristics, and communicates with an interrogator on an electromagnetic induction system without requiring any electric contact point.
2. Related Background Art
Recently, contactless data carriers, such as tags or IC cards including IC chips with the required circuits integrated therein for thickness and size reductions, have been developed that transmit/receive data or supply/receive power using electromagnetic induction coupling or the like without using electric contact points. Besides the characteristics of having a high storage capacity and an advanced security function, the contactless data carriers have characteristics that, for example, communication can be carried out simply by inserting the tags or IC cards themselves into slots or bringing them close to an antenna part of a reader-writer. Hence, the contactless data carriers require no mechanical part such as contact points and thus are maintenance-free. Consequently, they can be attached to removable components used in equipment or used for merchandise or process control and allow the components to be controlled or to be used under optimum conditions. Such a contactless data carrier transmits information to and receives information from an interrogator as a reader-writer using a medium such as a radio wave. The electric power required for the operations of a control circuit and a memory unit of the contactless data carrier is obtained through rectification of an induced current generated by an electromagnetic induction operation in a coil provided inside the contactless data carrier by a radio wave transmitted from the interrogator.
A configuration of a conventional contactless data carrier is described with reference to FIG. 7.
As shown in FIG. 7, a conventional contactless data carrier has a configuration in which an electronic circuit module including an antenna coil 2 and an integrated circuit 4 placed on a circuit board 3 is provided inside a resin case 1 and a sheet-like resin case 5. The integrated circuit 4 includes a diode circuit, a demodulator circuit, a power circuit, a modulation circuit, and a memory and control circuit.
The antenna coil 2 is produced with a copper wire wound a plurality of times in a rectangular or circular shape. The integrated circuit 4 used for controlling communication with an interrogator (not shown in the figure) is bonded to the circuit board 3 and is connected electrically to the antenna coil 2 on the circuit board 3. FIG. 7 shows a schematic view of the antenna coil 2 formed of a bundled coil.
Conventionally, the resin case 1 of the contactless data carrier generally is formed by injection molding of molding resin. This is carried out by injection molding in the following procedure. That is, the antenna coil 2 and the circuit board 3 with the integrated circuit 4 mounted thereon are placed on the sheet-like resin case 5, this resin case 5 is inserted into a cavity of a molding die, and then resin is injected into the die.
In this case, the resin case 1 is molded to be packaged as a part of the contactless data carrier. In order to prevent positional shifts from being caused by the pressure of the molding resin when the resin is injected into the die, the antenna coil 2 and the circuit board 3 may be fixed to the sheet-like resin case 5 by pasting or the like in some cases.
However, in the conventional manufacturing method by injection, the integrated circuit 4, the circuit board 3, and the antenna coil 2 are exposed to high temperatures and high pressure of the molding resin in the molding step. As a result, defects such as breakage of the integrated circuit 4, disconnection of the antenna coil 2, or the like may occur in some cases.
In addition, it was difficult to carry out the molding without causing a pinhole between the sheet-like resin case 5 and the resin case 1. When the pinhole is in contact with the antenna coil 2 or the integrated circuit 4 of the electronic circuit module, the electrostatic withstand voltage characteristic cannot be secured reliably, which has been a problem.
The present invention solves the above-mentioned problems. It is an object of the present invention to provide a contactless data carrier, having an excellent electrostatic withstand voltage characteristic, and whose interior is not exposed to high temperatures and high pressure in molding the contactless data carrier.
In order to solve the aforementioned problems, a contactless data carrier of the present invention includes an electronic circuit module contained in a hollow resin case provided with a first slit. The electronic circuit module includes an antenna coil and an integrated circuit electrically connected to each other.
According to this configuration, since the electronic circuit module is contained inside the hollow resin case, the integrated circuit and the antenna coil are not exposed to high temperatures and high pressure in forming the contactless data carrier as in the injection molding. Therefore, defects such as the breakage of the integrated circuit or the disconnection in the antenna coil can be avoided. In addition, since the first slit leading into the hollow portion inside the resin case is provided, it is possible to prevent the occurrence of the problem that the resin case swells due to the increase in air pressure inside the resin case under a high temperature state and thus the registration between the outer face of the resin case and an antenna coil of a reader-writer deteriorates and the communication characteristics deteriorate accordingly. Furthermore, since the slit is provided in the hollow resin case, the pressure inside the case does not increase, so that pinholes do not tend to be formed during the fusion of the resin case and thus the electrostatic withstand voltage characteristic can be improved.
Preferably, the contactless data carrier of the present invention further includes a shielding plate provided between the electronic circuit module and the first slit, and the shielding plate is provided with a second slit.
According to this configuration, the creeping distance from the first slit to the electronic circuit module can be increased, so that the electrostatic withstand voltage performance further can be improved.
Preferably, in the contactless data carrier according to the present invention, the antenna coil and the integrated circuit are provided on a single board.
With this configuration, an electronic circuit module with the antenna coil, integrated circuit, and board combined to form one unit can be configured. Thus, the fixing of the electronic circuit module to the resin case can be facilitated.
In the contactless data carrier according to the present invention, it is preferable that the resin case is formed by allowing a first part and a second part to join each other and the first slit is provided in a portion where the first part and the second part join each other.
According to this configuration, a cut portion is preformed in the first part or the second part and thus the first slit can be provided in the resin case easily.
In the contactless data carrier according to the present invention, it is preferable that the electronic circuit module is positioned close to one face inside the resin case and the first slit is provided in a face opposing the one face of the resin case.
With this configuration, the position of the first slit can be kept away from the electronic circuit module, so that the electrostatic withstand voltage characteristic can be improved.
Furthermore, in the contactless data carrier according to the present invention, it is preferable that a plurality of shielding plates are provided between the electronic circuit module and the first slit and each of the shielding plates is provided with a slit.
According to this configuration, since the creeping distance from the first slit to the antenna coil can be increased, the electrostatic withstand voltage characteristic can be improved.